Radio Transmission in Water
The Jacky's email (remove spam text)
Water conducts sound extremely well , better (and faster) than air.
I thinking in a very free form mode here but you could rip the
transducers off a couple of old fish finders and use em for tx and rcv.
I think these guys operate above 30 KHz. You may be able to modulate
enough info on to the carrier to do slow frame video.
See also: massmind.org/techref/index.htm?key=